In the processing of nutritional products, generally there have been two approaches to packaging a nutritional product in a container. The first method utilizes retorting, whereby a nutritional product is placed in a container; the container is sealed; and then the product and container are subjected to heat, such that the product is sterilized. In the second method, hereinafter referred to an aseptic processing, a container is subjected to a sterilizing process prior to its receiving a sterilized nutritional product. An apparatus and method for sterilizing containers for aseptic processing is taught, for example, in U.S. Pat. No. 5,007,232.
A preferred aseptic processing system for nutritional products will operate continuously for sixteen hours (2 shifts) with eight hours (1 shift) for cleaning and sterilization. In order for an aseptic processing system to be cost effective the minimum run time acceptable is eight hours. When a milk based liquid nutritional product for infants was processed in a prototype aseptic processing system using a Ultra High Temperature Short Time (hereinafter refer to as "UHTST") treatment an almost immediate fouling (less than 30 minutes) of the hold tube occurred. This fouling problem was severe enough to require the UHTST unit to be shut down and cleaned before further processing could be attempted. As used herein and in the claims UHTST treatment means elevating the temperature of a liquid nutritional product to a temperature of at least 132.degree. C. and holding the product at this high temperature for a time sufficient to commercially sterilize the product.
The major problems with fouling and "burn-on" in a UHTST system are: (a) that the fouling material acts as a barrier to heat transfer thereby reducing the effectiveness of the UHTST system; and (b) narrows the internal diameter of the hold tube, which increases the product velocity, thereby reducing the hold time sterilization. As the fouling material begins to inhibit the heating of the liquid nutritional product the system responds by increasing the steam pressure to compensate. This increase in steam pressure accelerates the rate of fouling and in a short time the system loses the capacity to maintain sterilization temperatures and hold times. Only by reducing or eliminating the amount of "burn-on" and fouling of a milk based liquid nutritional product can UHTST system operate effectively for an acceptable length of time.
It is clear that a need exists for a method of solving the problem of fouling or "burn-on" which occurs in a UHTST system when processing a milk based liquid nutritional product for infants.